Tire

Abstract

To provide a tire capable of improving straight traveling performance and turning performance on a wet road surface in a well-balanced manner.SOLUTION: At least one row of a plurality of rows of land portions 30 formed in a tread portion 1 is a convex rib 32 continuously extending along a tire circumferential direction and having a shape in which a contour line of a tread in a tire meridian cross-sectional view in an unloaded state in which the tire is mounted on a regular rim and a regular internal pressure is applied bulges outward in a tire radial direction, and the contour line of the tread of the convex rib 32 is constituted by a curve defined by a function of Expression (1) or (2).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire having rib-shaped land portions extending continuously in the tire circumferential direction, and more particularly to a tire that enables a balanced improvement in straight-line running performance and cornering performance on wet road surfaces. [Background technology]

[0002] To improve wet tire performance, a technology is known in which the contact surface of the land portion formed in the tread portion is partially bulged outward in the tire radial direction from the reference contour line of the tread profile (see, for example, Patent Document 1). In such tires, the bulged land portion increases the ground contact pressure at the bulged land portion, improving wet performance (especially straight-line performance when traveling on wet roads). However, there is a concern that the bulged land portion reduces the ground contact pressure at the tire width direction ends (non-bulged portions) of the land portion, which may result in insufficient cornering performance on wet roads. Therefore, there is a need for a measure to improve straight-line performance and cornering performance on wet roads in a balanced manner. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-100170 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can improve straight-line running performance and cornering performance on wet road surfaces in a well-balanced manner. [Means for solving the problem]

[0005] In order to achieve the above object, the tire of the present invention provides a tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, the tread portion having at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions partitioned by the circumferential main grooves, at least one row of the plurality of land portions extending continuously along the tire circumferential direction, a convex rib having a shape in which the outline of the tread surface in a meridian cross section of the tire when mounted on a normal rim and given a normal internal pressure and in an unloaded state bulges outward in the tire radial direction, one end of the convex rib in the tire width direction is designated by point p1, the other end of the convex rib in the tire width direction is designated by point p2, and the line segment connecting points p1 and p2 is defined as a straight line P, the point on the contour line of the convex rib that is the longest from the line P is defined as point p3, and the intersection of the line P and a perpendicular line to the line P that passes through point p3 is defined as point p4; when the contour line of the tread surface of the convex rib is viewed as a curve in XY coordinates with point p4 as the origin, where the line connecting points p3 and p4 is defined as the Y axis and the line connecting points 1 and p2 is defined as the X axis, 80% or more of the length of the portion of the contour line of the tread surface of the convex rib on one side of point p3 in the tire width direction is formed by a curve defined by the function of formula (1) or (2) below.

number

number

[0006] In order to improve wet performance, the tire of the present invention is provided with a convex rib in which the outline of the tread in a tire meridian cross section bulges outward in the tire radial direction, and because this convex rib has the characteristics described above, the bulging shape of the convex rib is favorable, enabling a balanced improvement in straight-line running performance and cornering performance on wet roads. That is, the tire width direction ends of the convex rib (near point p3) do not bulge relative to the vicinity of point p3, thereby suppressing a decrease in ground contact pressure and ensuring good cornering performance on wet roads.

[0007] In the present invention, it is preferable to satisfy the relationships 0.8≦n / m≦1.2, 1.5≦n≦5, and 1.5≦m≦5. This improves the bulging shape of the convex rib, which is advantageous for improving straight-line running performance and cornering performance on wet road surfaces in a balanced manner.

[0008] In the present invention, it is preferable to satisfy the relationship 0.001≦b / (ap+ap′)≦0.25, which improves the bulging shape of the convex rib and is advantageous for improving straight-line running performance and cornering performance on wet roads in a balanced manner.

[0009] In the present invention, it is preferable to satisfy the relationship 0.05 mm≦b≦2.0 mm, which improves the bulging shape of the convex rib and is advantageous for improving straight-line running performance and cornering performance on wet roads in a balanced manner.

[0010] In the present invention, it is preferable that point p3 be located within a range of 30% of the length W of said straight line P on both sides in the tire width direction from the midpoint of said straight line P. This causes the central portion of the convex rib to bulge the most (point p3 where the convex rib bulges the most is located near the center of the convex rib in the tire width direction), which promotes drainage over the rib and is advantageous for improving wet performance.

[0011] In the present invention, the hardness Hs of the tread rubber constituting the tread portion is preferably 55 or more and 78 or less. By having such an appropriate hardness, the bulging shape of the convex ribs is well maintained during running, and the effects of the convex ribs described above can be efficiently exhibited.

[0012] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof can be filled with air, an inert gas such as nitrogen, or other gases. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a meridian cross-sectional view of a tire according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram schematically showing a convex rib of a tire according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0015] When the tire of the present invention is a pneumatic tire as shown in FIG. 1, it comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In FIG. 1, the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using FIG. 1 will be based basically on the meridian cross-section shape shown, but each tire component also extends in the tire circumferential direction and forms an annular shape.

[0016] A carcass layer 4 is installed between a pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and folded back from the inner side to the outer side in the tire width direction around a bead core 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of the bead core 5, and this bead filler 6 is wrapped by the main portion and folded back portion of the carcass layer 4. Meanwhile, a plurality of belt layers 7 (two layers in FIG. 1 ) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Furthermore, at least one belt reinforcing layer 8 (two layers in FIG. 1 ) is provided on the outer periphery of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction.

[0017] A tread rubber layer 11 is disposed on the outer peripheral side of the carcass layer 4 in the tread portion 1, a side rubber layer 12 is disposed on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the bead portion 3. The tread rubber layer 11 has a structure in which two types of rubber layers with different physical properties (a cap tread layer 11C that forms the tread surface of the tread portion 1 and an under tread layer 11U disposed on its inner peripheral side) are laminated in the tire radial direction.

[0018] As described below, the present invention relates to the tread portion 1 of the tire (particularly the cross-sectional shape of the convex ribs, etc., described below), and therefore the basic structure of the tire is not limited to the general structure described above. Also, the following description will be based on the pneumatic tire shown in Fig. 1, etc., but the present invention can be applied to various tires, including non-pneumatic tires, as long as they have a surface that comes into contact with the road surface (a portion corresponding to the surface of the tread portion 1 in a pneumatic tire) and have land portions (convex ribs) formed thereon.

[0019] As shown in FIG. 1 , at least two circumferential main grooves 20 (four in the example of FIG. 1 ) extending linearly along the tire circumferential direction are provided on the surface of the tread portion 1 of the tire of the present invention. These at least two circumferential main grooves 20 define multiple rows (five in the example of FIG. 1 ) of land portions 30 extending along the tire circumferential direction. In the following description, a pair of land portions 30 located on the tire widthwise outer side of a pair of circumferential main grooves 20 located on the outermost side in the tire width direction may be referred to as shoulder land portions 31. In the present invention, at least one row of these land portions 30 (one row in FIG. 1 ) is configured as a convex rib 32 described below. Note that when the land portions 30 other than the shoulder land portions 31 are convex ribs 32, the land portions 30 (convex ribs 32) are defined by a pair of circumferential main grooves 20, and therefore a profile shape described below is applied to the top surface (tread surface) of the land portion 30 (convex rib 32) sandwiched between the pair of circumferential main grooves 20. When the shoulder land portion 31 is a convex rib 32, the shoulder land portion 31 (convex rib 32) is defined on the tire widthwise outer side of the circumferential main groove 20, so the profile shape described below is applied to the top surface (tread surface) of the shoulder land portion 31 (convex rib 32) sandwiched between the circumferential main groove 20 and the ground contact edge.

[0020] The convex rib 32 is a land portion having a shape in which the outline of the tread bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim, normal internal pressure is applied, and no load is applied, as shown in Fig. 2. Although not depicted in Fig. 2 because both are tire meridian cross sections, the convex rib 32 has a shape that extends continuously in the tire circumferential direction without being interrupted by lateral grooves extending in the tire width direction.

[0021] "Regular rim" refers to the rim specified for each tire by the standard system, including the standard on which the tire is based, such as the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. "Regular internal pressure" refers to the air pressure specified for each tire by the standard system, including the standard on which the tire is based, such as the maximum air pressure for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and the "INFLATION PRESSURE" for ETRTO.

[0022] 2, for this convex rib 32, one end of the convex rib 32 in the tire width direction is defined as point p1, the other end of the convex rib 32 in the tire width direction is defined as point p2, the line segment connecting points p1 and p2 is defined as line P, the point on the contour of the convex rib 32 that is the greatest distance from line P is defined as point p3, and the intersection of line P and the perpendicular to line P passing through point p3 is defined as point p4. Based on points p1 to p4 defined in this way, an XY coordinate system is assumed in which the line connecting points p3 and p4 is defined as the Y axis, the line connecting points 1 and p2 is defined as the X axis, and point p4 is defined as the origin. When the contour of the tread of the convex rib 32 is viewed as a curve on this XY coordinate system, the contour of the tread of the convex rib 32 of the present invention is composed of a curve defined by a function of the following formula (1) or (2) on one side of point p3 in the tire width direction.

[0023]

number

[0024]

number

[0025] In the above formulas (1) and (2), a is the radius of the major axis of the curve defined by the function of formula (1) on the X-axis on the side of point p1 relative to point p4, and satisfies the relationship ap≦a≦ap×1.5, where ap is the distance between points p1 and p4; a' is the radius of the major axis of the curve defined by the function of formula (2) on the X-axis on the side of point p2 relative to point p4, and satisfies the relationship ap'≦a'≦ap'×1.5, where ap' is the distance between points p2 and p4; b is the radius of the minor axis of the curve defined by the function of formula (1) or (2) on the Y-axis on the side of point p3, and matches the distance between points p3 and p4, and satisfies the relationship 0.001≦b / a≦0.45 or 0.001≦b / a'≦0.45; and n≧1.5, m≧1.5, and y>0.

[0026] In the present invention, it is not necessary for the entire contour line of the tread surface of the convex rib 32 to be configured as a curve defined by the function of formula (1) or (2) above, and 80% or more, preferably 82% or more, of the length of the portion of the contour line of the tread surface of the convex rib 32 on one side of point p3 in the tire width direction is configured as a curve defined by the function of formula (1) or (2) above. For example, in Figure 2, the curve (ellipse) defined by the function of formula (1) or (2) above is shown by a dashed line, and although the shapes do not match at the tire width direction end portions of the tread surface of the convex rib 32, the curve (dashed line in the figure) defined by the function of formula (1) or (2) above and the contour line of the tread surface of the convex rib 32 match on the center side in the tire width direction, including point p3.

[0027] Such a bulging shape increases the contact pressure near point p3 where the convex rib 32 bulges most, thereby improving straight-line running performance when traveling on wet roads. On the other hand, because the outline of the tread of the convex rib 32 is formed by a curve defined by the function of formula (1) or (2) above, the tire width direction ends of the convex rib 32 (near points p1 and p2) do not drop excessively relative to point p3, and contact pressure is ensured even at the tire width direction ends of the convex rib 32, allowing for good cornering performance on wet roads.

[0028] In the present invention, it is sufficient that at least one of the plurality of land portions is a convex rib 32 that satisfies the above-mentioned conditions, and therefore the other land portions 30 may be land portions (conventional general land portions) whose tread contour line does not bulge outward in the tire radial direction in a meridian cross section of the tire when mounted on a regular rim, with regular internal pressure applied, and in an unloaded state. They may also be land portions whose bulging shape is not constituted by a curve defined by the function of the above formula (1) or (2) (an arc-shaped contour line having a single radius of curvature).

[0029] Note that points p1 and p2 are both ends of the tread surface of the convex rib 32, and are defined as points (edges of the convex rib 32) where the side surface of the convex rib 32 (wall surfaces of the adjacent circumferential main grooves) and the tread surface of the convex rib 32 connect. If the edges of the convex rib 32 are chamfered, the end points of the chamfer on the tread surface side become points p1 and p2.

[0030] In the above formulas (1) and (2), if a or a' is less than ap or ap', sufficient ground contact pressure cannot be obtained at the tire width direction ends of the convex ribs 32, and the effect of improving cornering performance on wet road surfaces will be limited. If a or a' exceeds ap × 1.5 or ap' × 1.5, the convex ribs 32 will not expand sufficiently and sufficient ground contact pressure cannot be obtained at the tire width direction ends of the convex ribs 32, and the effect of improving cornering performance on wet road surfaces will be limited. The above a, a', ap, and ap' preferably satisfy the relationships ap≦a≦ap × 1.2 and ap'≦a'≦ap' × 1.2.

[0031] In the above formulas (1) and (2), if b / a or b / a' is less than 0.001, the bulging amount of the convex rib 32 becomes excessive, the contact area decreases, and straight-line running performance and cornering performance on wet roads cannot be sufficiently ensured. If b / a or b / a' exceeds 0.45, the bulging amount of the convex rib 32 becomes too small, and sufficient contact pressure cannot be obtained at the tire width direction ends of the convex rib 32, limiting the effect of improving cornering performance on wet roads. Furthermore, sufficient contact pressure cannot be maintained at the center of the convex rib 32, resulting in reduced drainage, which may also reduce straight-line running performance on wet roads. Preferably, the above b / a or b / a' satisfies the relationship 0.002≦b / a≦0.40 or 0.002≦b / a'≦0.40.

[0032] In the above formulas (1) and (2), n and m satisfy the relationships n≧1.5 and m≧1.5, preferably 1.5≦n≦5 and 1.5≦m≦5, more preferably 2≦n≦4 and 2≦m≦4, and even more preferably 2≦n≦3 and 2≦m≦3. In the above formulas (1) and (2), the larger n and m are, the smaller the difference in the amount of expansion between the center and the tire widthwise ends of the convex rib 32. This allows for improved contact pressure at the tire widthwise ends of the convex rib 32, thereby improving cornering performance on wet roads while maintaining straight-line performance on wet roads. In particular, setting n and m within the above-described ranges improves the expansion shape of the convex rib 32, which is advantageous for achieving a balanced improvement in straight-line performance and cornering performance on wet roads. If n and m are less than 1.5, the tire widthwise ends of the convex rib 32 will sag significantly, limiting the effect of improving contact pressure at the tire widthwise ends of the convex rib 32. If n and m exceed 5, the difference in the amount of expansion between the center of the convex rib 32 and the tire widthwise end becomes too small, the expansion of the center of the convex rib 32 becomes insufficient, and it becomes difficult to maintain sufficient ground contact pressure at the center of the convex rib 32.

[0033] In addition to the above-mentioned n and m satisfying the above-mentioned ranges, the ratio n / m preferably satisfies the relationship 0.8≦n / m≦1.2, more preferably 0.9≦n / m≦1.1. This improves the bulging shape of the convex rib 32, which is advantageous for improving straight-line running performance and cornering performance on wet roads in a balanced manner. If the ratio n / m is below the above-mentioned range, the contact pressure at the tire widthwise ends of the convex rib 32 increases, limiting the effect of improving straight-line running performance on wet roads. If the ratio n / m exceeds the above-mentioned range, the difference in the amount of bulging between the center portion of the convex rib 32 and the tire widthwise ends becomes too small, resulting in insufficient bulging at the center portion of the convex rib 32 and making it difficult to maintain sufficient contact pressure at the center portion of the convex rib 32.

[0034] In the above formulas (1) and (2), the distance ap between points p1 and p4, the distance ap' between points p2 and p4, and the distance b between points p3 and p4 preferably satisfy the relationship 0.001≦b / (ap+ap')≦0.25, more preferably 0.001≦b / (ap+ap')≦0.25. The sum of distances ap and ap' (ap+ap') essentially corresponds to the width of the convex rib 32, and distance b corresponds to the amount of bulging from the line P connecting points p1 and p2. This allows the amount of bulging of the convex rib 32 relative to the width of the convex rib 32 to be set within an appropriate range, resulting in a favorable bulging shape of the convex rib 32 and advantageously improving straight-line running performance and cornering performance on wet roads in a balanced manner. If b / (ap+ap') is less than 0.001, the bulging of the center of the convex rib 32 will be insufficient, making it difficult to maintain sufficient ground contact pressure at the center of the convex rib 32. If b / (ap+ap') exceeds 0.25, the protruding amount of the convex rib 32 becomes excessive, the contact area cannot be sufficiently secured, and the effect of improving cornering performance and straight-line performance on wet road surfaces becomes limited.

[0035] In addition to the above relationship, the distance b preferably satisfies the relationship 0.05 mm≦b≦2.0 mm, more preferably 0.05 mm≦b≦1.5 mm. This improves the bulging shape of the convex rib, which is advantageous for achieving a balanced improvement in straight-line running performance and cornering performance on wet roads. If the distance b is less than 0.05 mm, the bulge at the center of the convex rib 32 is insufficient, making it difficult to maintain sufficient ground contact pressure at the center of the convex rib 32. If the distance b exceeds 2.0 mm, the amount of bulge of the convex rib 32 becomes excessive, making it impossible to ensure a sufficient contact area, limiting the effect of improving cornering performance and straight-line running performance on wet roads.

[0036] As described above, the sum of the distance ap and the distance ap' (ap+ap') corresponds to the width of the protruding rib 32, and can be set appropriately depending on the tire size and tread pattern. There are no particular limitations on the range, but ap+ap' can be set to, for example, 10 mm to 50 mm.

[0037] As described above, point p3 is the point on the contour of the convex rib 32 where the distance to the line P connecting points p1 and p2 is greatest, and corresponds to the maximum bulge point of the convex rib 32. This point p3 is preferably located within a range of 30%, more preferably 25%, and even more preferably 20% of the length W of line P on both sides of the midpoint of line P in the tire width direction. This allows the central portion of the convex rib 32 to bulge the most (point p3 where the convex rib 32 bulges the most is located near the center of the convex rib 32 in the tire width direction), which promotes drainage on the convex rib 32 and is advantageous for improving wet performance. If point p3 is located outside the above range, the point where the convex rib 32 bulges the most (point p3) will be unevenly located at the end of the convex rib in the tire width direction, making it difficult to ensure good drainage performance and limiting the effect of improving straight-line running performance and cornering performance on wet roads.

[0038] In the above-mentioned convex rib 32, the groove depth of a pair of adjacent circumferential main grooves 20 is preferably 80% or more of the groove depth of the deepest circumferential main groove 20. Since land portions where the groove depth of adjacent circumferential main grooves 20 is large (i.e., land portions that protrude from the groove bottom to a large extent) are greatly affected by ground contact pressure, application of the above-mentioned convex rib 32 can effectively improve straight-line running performance and cornering performance on wet road surfaces.

[0039] The convex rib 32 has a shape that extends continuously in the tire circumferential direction without being interrupted by lateral grooves extending in the tire width direction, but may also have narrow grooves or sipes with a groove width of 3 mm or less. The provision of these narrow grooves or sipes ensures the drainage and edge effects of the narrow grooves and sipes, which is advantageous for improving straight-line performance and cornering performance on wet roads. Note that, because the narrow grooves and sipes have a small groove width as mentioned above, the provision of these narrow grooves and sipes means that the convex rib 32 is considered to be uninterrupted.

[0040] Regarding the tread portion 1 configured as described above, the hardness Hs of the tread rubber (rubber constituting the tread rubber layer 11) constituting the tread portion 1 is preferably 55 or more and 78 or less, more preferably 58 or more and 75 or less, and even more preferably 58 or more and 72 or less. When the tread rubber layer includes a cap tread layer 11C and an undertread layer 11U as shown in FIG. 1 , at least the cap tread layer 11C is preferably made of rubber having the above-mentioned hardness. Having the tread portion 1 with an appropriate hardness allows the protruding shape of the convex ribs 32 to be well maintained during running, allowing the above-described effects of the convex ribs 32 to be efficiently exhibited. If the hardness Hs is less than 55, the tread rubber is too soft, and therefore the protruding shape of the convex ribs 32 cannot be adequately maintained when deformed by lateral force during running, limiting the effect of uniforming ground pressure. If the hardness Hs exceeds 78, the tread rubber is too hard, and the ground pressure of the convex ribs 32 may increase locally, limiting the effect of uniforming ground pressure. The rubber hardness of the tread rubber is determined in accordance with JIS K6253 and is measured at a temperature of 20°C using a durometer type A.

[0041] The tire of the present invention (particularly a pneumatic tire) can be manufactured by a general manufacturing method. That is, the tread portion 1 including the above-mentioned convex rib 32 is molded using a tire mold. In this case, since it is practically difficult to manufacture the convex rib 32 having a contour line that perfectly matches the curve defined by the function of the above formula (1) or (2), even a convex rib 32 having a contour line that approximates the curve defined by the function of the above formula (1) or (2) by combining multiple arcs and / or straight lines with a length of 0.5 mm or less can be considered to satisfy the above-mentioned conditions of the present invention.

[0042] The protruding rib 32 may have multiple bulging portions. That is, point p3 may exist at multiple locations in the tire width direction. In this case, points p3 and p4 can be defined for each bulging portion, and the Y axis can be set at each bulging portion, so that each bulging portion can have the above-described contour line of the present invention based on this.

[0043] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0044] The tire size is 235 / 60R18, and the basic structure (cross-sectional structure) is shown in FIG. 1 . Regarding the convex rib, the end of one side of the convex rib in the tire width direction is defined as point p1, the end of the other side of the convex rib in the tire width direction is defined as point p2, the line segment connecting points p1 and p2 is defined as a straight line P, the point on the contour line of the convex rib that is the longest from line P is defined as point p3, and the intersection of line P and the perpendicular to line P passing through point p3 is defined as point p4. When the contour line of the tread surface of the convex rib is viewed as a curve in XY coordinates with point p4 as the origin, the straight line connecting points p3 and p4 is defined as the Y axis, the straight line connecting points 1 and p2 is defined as the X axis, and the ratio a / ap of the radius a on the point p1 side of point p4 on the X axis of the major axis of the curve defined by the function of equation (1) above to the distance a p between point p1 and point p4 is defined by the function of equation (2) above. Tables 1 to 3 show the settings of pneumatic tires (test tires) for Conventional Example 1 and Examples 1 to 24, respectively. The settings of Conventional Example 1 and Examples 1 to 24 are as follows: the ratio a' / ap' of the radius a' on the side of point p2 from point p4 on the X axis of the major axis of the curve to the distance ap' between point p2 and point p4; the ratio b / a of the distance b between point p3 and point p4 to the radius a; the ratio b / a' of the distance b to the radius a'; m in the above-mentioned formula (1) or (2); n in the above-mentioned formula (1) or (2); the ratio n / m; the ratio b / (ap+ap') of the distance b to the sum of the distances ap and ap'; the distance b; the ratio of the distance from the midpoint of line P to point p3 in the tire width direction to the length W of line P (the "position of p3" in the table, unit: %); and the hardness Hs of the tread rubber (cap tread rubber) that constitutes the tread portion.

[0045] The values ​​in the table are based on the contour line of the tread surface of the convex rib in a meridian cross section of a tire mounted on a standard rim and pressurized to the standard internal pressure, without load. "Hardness Hs" is a value measured at 20°C using a durometer type A in accordance with JIS K6253.

[0046] Conventional example 1 is an example in which the contour line of the tread surface of the convex rib is composed of a single arc with a curvature radius of 880 mm. In this case, points p1 to p4 can be defined, so the corresponding values ​​can be entered for the ratio b / (ap+ap'), distance b, and "position of p3" in the table. However, because this contour line does not satisfy formulas (1) and (2), the ratios a / ap, a' / ap', b / a, b / a', m, n, and n / m are left blank.

[0047] The straight running performance and cornering performance on wet road surfaces of these test tires were evaluated by the following evaluation methods, and the results are shown in Tables 1 to 3.

[0048] Straight-line performance on wet roads Each test tire was mounted on a standard rim (rim size 18 x 7J), inflated to an internal pressure of 250 KPa (standard internal pressure for passenger cars), and fitted to all wheels of a test vehicle (a passenger car with an engine displacement of 2000 cc). The vehicle was driven on a test course consisting of a wet road at a speed of 60 km / h, and five test drivers performed a sensory evaluation of the driving performance when driving on a straight road. The evaluation results were calculated by adding up the scores of the five drivers and are shown in the "Straight-line performance" column in the table as an index, with Conventional Example 1's value being 100. A higher index value means better straight-line performance on wet roads.

[0049] Turning performance on wet roads Each test tire was mounted on a standard rim (rim size 18 x 7J), inflated to an internal pressure of 250 KPa (standard internal pressure for passenger cars), and fitted to all wheels of a test vehicle (a passenger car with an engine displacement of 2000 cc). The vehicle was driven on a test course consisting of a wet road surface at a speed of 60 km / h, and five test drivers performed a sensory evaluation of the cornering performance when entering a corner. The evaluation results were calculated by adding up the scores of the five drivers and are shown in the "Cornering Performance" column in the table as an index, with Conventional Example 1 having a value of 100. A higher index value means better cornering performance on wet road surfaces.

[0050] [Table 1]

[0051] [Table 2]

[0052] [Table 3]

[0053] As is clear from Tables 1 to 3, the tires of Examples 1 to 24 improved at least one of the straight-line running performance and cornering performance on wet road surfaces compared to Conventional Example 1, and achieved a good balance between these performances.

[0054] The present disclosure includes the following inventions. Invention [1] A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion includes at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions defined by the circumferential main grooves, At least one row of land portions among the plurality of land portions extends continuously along the tire circumferential direction, and is a convex rib having a shape in which the outline of the tread surface bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim and has a regular internal pressure applied and is in an unloaded state, An end portion of the convex rib on one side in the tire width direction is defined as point p1, an end portion of the convex rib on the other side in the tire width direction is defined as point p2, a line segment connecting point p1 and point p2 is defined as a straight line P, a point on the contour line of the convex rib that is the longest from the straight line P is defined as point p3, and an intersection point between the straight line P and a perpendicular line to the straight line P that passes through point p3 is defined as point p4. When the outline of the tread surface of the convex rib is viewed as a curve of XY coordinates with the line connecting the point p3 and the point p4 as the Y axis, the line connecting the point 1 and the point p2 as the X axis, and the point p4 as the origin, A tire characterized in that, on one side of point p3 in the tire width direction of the contour line of the tread surface of the convex rib, 80% or more of the length of the portion on the one side of point p3 in the tire width direction of the contour line of the tread surface of the convex rib is formed by a curve defined by a function of the following formula (1) or (2):

number

number

[0055] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Belt reinforcement layer 11 Tread rubber layer 11C cap tread rubber layer 11U Undertread rubber layer 12 Side rubber layer 13 Rim cushion rubber layer 20 Circumferential main groove 30 Land 31 Shoulder Land Section 32 Convex rib CL Tire Equator

Claims

1. A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion includes at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions defined by the circumferential main grooves, At least one row of land portions among the plurality of land portions extends continuously along the tire circumferential direction, and is a convex rib having a shape in which the outline of the tread surface bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim and has a regular internal pressure applied and is in an unloaded state, An end portion of the convex rib on one side in the tire width direction is defined as point p1, an end portion of the convex rib on the other side in the tire width direction is defined as point p2, a line segment connecting point p1 and point p2 is defined as a straight line P, a point on the contour line of the convex rib that is the longest distance from the straight line P is defined as point p3, and an intersection point between the straight line P and a perpendicular line to the straight line P that passes through point p3 is defined as point p4. When the outline of the tread surface of the convex rib is viewed as a curve of XY coordinates with the line connecting the points p3 and p4 as the Y axis, the line connecting the points 1 and p2 as the X axis, and the point p4 as the origin, A tire characterized in that, on one side of point p3 in the tire width direction of the contour line of the tread surface of the convex rib, 80% or more of the length of the portion on the one side of point p3 in the tire width direction of the contour line of the tread surface of the convex rib is formed by a curve defined by a function of the following formula (1) or (2): [Equation 1] [Equation 2] (In the above formulas (1) and (2), a is a radius of the major axis of the curve defined by the function of formula (1) on the X-axis closer to point p1 than point p4, and satisfies the relationship ap≦a≦ap×1.5 with respect to the distance ap between point p1 and point p4, a' is a radius of the major axis of the curve defined by the function of formula (2) on the X-axis closer to point p2 than point p4, and satisfies the relationship ap'≦a'≦ap'×1.5 with respect to the distance ap' between point p2 and point p4, b is a radius of the minor axis of the curve defined by the function of formula (1) or (2) on the Y axis closer to point p3 than point p4, and b coincides with the distance between point p3 and point p4, and satisfies the relationship 0.001≦b / a≦0.45 or 0.001≦b / a′≦0.45; The relationships n ≧ 1.5, m ≧ 1.5, and y > 0 are satisfied.

2. 2. The tire according to claim 1, wherein the relationships 0.8≦n / m≦1.2, 1.5≦n≦5, and 1.5≦m≦5 are satisfied.

3. 3. The tire according to claim 1, wherein the relationship of 0.001≦b / (ap+ap′)≦0.25 is satisfied.

4. 3. The tire according to claim 1, wherein the relationship b satisfies 0.05 mm≦b≦2.0 mm.

5. 3. The tire according to claim 1, wherein the point p3 is located within a range of 30% of the length W of the straight line P on both sides of the midpoint of the straight line P in the tire width direction.

6. 3. The tire according to claim 1, wherein the hardness Hs of the tread rubber constituting the tread portion is 55 or more and 78 or less.

Images